Neutral gray, fixed tint sunglasses have been marketed for many years. Bausch and Lomb, Rochester, N.Y. has marketed a glass G15 since the 1940s and Corning Incorporated, Corning, N.Y. has marketed Code 8364, included within U.S. Pat. No. 2,688,561 (Armistead), since the 1950s. Corning has also manufactured a glass having a composition similar to that of G-15 under Code 8015. Analyses of 8015 and 8364, reported in terms of weight percent on the oxide basis, are recorded below.
______________________________________ 8015 8364 ______________________________________ SiO.sub.2 68.41 65.4 Al.sub.2 O.sub.3 0.51 2.0 Na.sub.2 O 8.81 7.25 K.sub.2 O 9.71 10.6 ZnO 6.76 13.52 Fe.sub.2 O.sub.3 5.54 1.7 Co.sub.3 O.sub.4 0.021 -- NiO 0.126 0.21 As.sub.2 O.sub.3 0.111 -- TiO.sub.2 -- 0.3. ______________________________________
Both of those glasses appear neutral gray to the eye when viewed alone. When they are examined side-by-side, however, Code 8015 glass appears greenish gray compared to Code 8364 glass. On the other hand, Code 8364 glass assumes a brownish gray hue when viewed next to a more neutral gray; i.e., a glass having a chromaticity closer to the Illuminant.
Recently, considerable effort has been directed at developing fixed tint lenses that are ultraviolet absorbing. In particular, such efforts have been directed at achieving glass lenses that transmit no more than one percent at 380 nm; that approach a true neutral gray as determined by Illuminant C; that avoid use of divalent metal oxides, particularly, CaO and ZnO; and that are chemically strengthenable. Glass compositions and lenses resulting from these efforts are described in recently issued U.S. Pat. Nos. 5,256,607 and 5,268,335 (Kerko et al.).
The glass compositions disclosed in the -607 patent consist essentially, expressed in terms of weight percent on an oxide basis, of
______________________________________ SiO.sub.2 65-72 CaO 0-1.5 B.sub.2 O.sub.3 2-6 Al.sub.2 O.sub.3 + CaO 0.2-2.25 Na.sub.2 O 6-10 As.sub.2 O.sub.3 0-0.3 K.sub.2 O 10-16 Fe.sub.2 O.sub.3 4.8-6.2 Na.sub.2 O + K.sub.2 O 17-23 Co.sub.3 O.sub.4 0.012-0.02 K.sub.2 O:Na.sub.2 O 1.25-2.25 NiO 0.16-0.21 Al.sub.2 O.sub.3 0-2.25 ZnO 0-1.5. ______________________________________
The compositions disclosed in the -335 patent, expressed in like manner, consist essentially of
______________________________________ SiO.sub.2 55-65 CaO 0-1.5 B.sub.2 O.sub.3 5-20 MgO 0-4 Al.sub.2 O.sub.3 4-10 TiO.sub.2 0-4 B.sub.2 O.sub.3 + Al.sub.2 O.sub.3 14-26 ZrO.sub.2 0-7 Li.sub.2 O 0-3 MgO + TiO.sub.2 + ZrO.sub.2 0-10 Na.sub.2 O 6-18 As.sub.2 O.sub.3 0-0.5 K.sub.2 O 2-10 ZnO 0-1.5 Li.sub.2 O + Na.sub.2 O + 13-22 Fe.sub.2 O.sub.3 3.5-5.5 K.sub.2 O Co.sub.3 O.sub.4 0.02-0.035 NiO 0.08-0.2. ______________________________________
These prior glasses have relied tin relatively high contents of iron oxide (Fe.sub.2 O.sub.3) to obtain the desired ultraviolet absorption. For color control, the oxides of cobalt and nickel have been employed in conjunction with the iron oxide. The oxides of calcium and zinc have been minimized to facilitate chemical strengthening and for environmental purposes.
The present invention is directed at glasses that provide significantly stronger ultraviolet absorption than that now available in prior glasses that rely on a high iron content. It provides lenses that are colored by transition metal oxides, and that exhibit a variety of unique chromaticities. Finally, it provides sunglass lenses capable of being chemically strengthened, that do not require CaO or ZnO, and that have optical properties at least equal to known sunglass lenses.